Injected beam crossed-field amplifier employing rf control of the injected beam current

ABSTRACT

An injected beam crossed-field amplifier is disclosed. The crossed-field tube includes a cylindrical nonemitting cathode sole electrode structure surrounded by a concentrically disposed slow wave anode circuit to define a magnetron-type interaction region in the annular space therebetween. An electron gun assembly is disposed at one end of the magnetron interaction region for injecting a beam of electrons into the magnetron interaction region axially thereof. A beam collector structure is disposed for collecting the electron beam after passage thereof through the magnetron interaction region. Radio frequency wave energy to be amplified is applied to the annular slow wave circuit, such circuit including a circuit sever to prevent reentrance of the wave energy on the circuit and to provide a drift space for debunching of the reentrant electron beam. By passing the electron beam through the magnetron interaction region to a collector structure, the dynamic range of the amplifier is extended down well into the low input signal regime, thereby providing an extremely wide dynamic range for the amplifier.

[72] lnventors George Berstei n Mlllburn; Hunter L. McDowell, Chatham,both of, NJ.

[21] Appl. No. 664,686

[22] Filed Aug. 31, 1967 [45] Patented July 13,197]

[54] INJECTED BEAM CROSSED-FIELD AMPLIFIER EMPLOYING RF CONTROL OF THEINJECTED BEAM CURRENT 4 Claims, 5 Drawing Figs.

[52] US. Cl 315/3951,

[51] Int. Cl ..H0lj 25/50,

HOlj 25/58 [50] Field ofSearch 315/393, 3.6, 3.5, 39.51

[56] References Cited UNITED STATES PATENTS 3,376,463 4/1968 Feinstein315/3951 3,433,992 3/1969 Tancredi et a1 3 l 5/3.6

CATHODE SUPPLY Primary Examiner-Richard A. Farley AssistanlExaminer-William T. Riflcin Attorneys-William J. Nolan and Leon F.Herbert ABSTRACT: An injected beam crossed-field amplifier is disclosed.The crossed-field tube includes a cylindrical nonemitting cathode soleelectrode structure surrounded by a concentrically disposed slow waveanode circuit to define a magnetron-type interaction region. in theannular space therebetween. An electron gun assembly is disposed at oneend of the magnetron interaction region for injecting a beam ofelectrons into the magnetron interaction region axially thereof. A beamcollector structure is disposed for collecting the electron beam afterpassage thereof through the magnetron interaction region. Radiofrequency wave energy to be amplified is applied to the annular slowwave circuit, such circuit including a circuit sever to preventreentrance of the wave energy on the circuit and to provide a driftspace for debunching of the reentrant electron beam. By passing theelectron beam through the magnetron interaction region to a collectorstructure, the dynamic range of the amplifier is extended down well intothe low input signal regime, thereby providing an extremely widedynamic: range for the amplifier.

ACCELERATOR J SUPPLY Billiiiil SUPPLY i SOLE . SUPPLY INJECTED BEAMCROSSED-FIELD AMPLIFIER EMPLOYING RF CONTROL OF THE INJECTED BEAMCURRENT In one embodiment of the present invention, a magnetroninjection type electron gun is employed. The magnetron gun isdimensioned to be closely spaced to the anode circuit and to berelatively open such that the RF fields from the slow wave circuit maypenetrate into the region of the electron gun. In

such a case, the injected beam current increases and decreases withincreases and decreases in the amplitude of the RF wave energy on thecircuit. Thus, when high power operation is required for amplifying highpower input signals the. RF fields control the injected beam intensityto supply more beam current. Conversely, when the tube is operating inthe relatively low signal regime the RF fields on the slow wave circuitare relatively weak and cause less beam current to be injected into themagnetron interaction region. As a result, the noise figure, which isproportional to the beam current, is improved in the low signal regimeand, in addition, the efficiency of the amplifier is improved in the lowsignal regime.

In another embodiment, an electron gun is provided of the magneticallyconfined flow -type having a relatively open accelerating beampassageway and being closely spaced to the anode circuit such that theRF fields from the anode circuit may penetrate into the region of theelectron gun for controlling the injected beam current in the manneraspreviously described.

DESCRIPTION OF THE PRIOR ART Heretofore, injected beam crossed-fieldamplifiers have been built having a beam of electronsflowing through theinteraction region orthogonally to the direction-of microwave power flowon the RF slow wave circuit. Such a tube. is described and claimed incopending U.S. Application Ser. No. 561,220, filed June 28, 1966, andassigned to the same assignee as the present invention. Such a tube hassubstantially improved operation in the low input power regime since theelectrons do not remain in the magnetron interaction region, but insteaddrift through theinteraction region andare collected on separatecollector electrodes. When the-electrons do not remain in the magnetroninteraction region the noise power in the beam is not coupled to thecircuit and, therefore, the tube may be operated in the low powerregime. The noise power which is coupled to the RF slow wave circuit isa function of the beam current, and therefore, in the low power regimeit is desirable to have a relatively low beam current whereas in thehigh power regime it is desired to have a relatively high beam currentsuch that relatively high power output may be obtained.

The prior art tube did not include means for controlling the injectedbeam current in accordance with the amplitude of the signal to beamplified. While it would be possible to detect the amplitude of thesignal to be amplified and to provide a control electrode forcontrolling the injected beam current in accordance with the intensityof the detected signal to be amplified, such an arrangement would berelatively complicated and expensive. Therefore, it is desired to obtaina simple means for controlling the injected beam current in accordancewith the amplitude of the RF signal to be amplified.

SUMMARY OF THE PRESENT INVENTION The principal object of the presentinvention is the provision of an improved injected beam crossed-fieldamplifier of the type wherein the injected beam is caused todriftthrough the magnetron interaction region to a beam collectorstructure.

One feature of the present invention is the provision, in an injectedbeam crossed-field amplifier of the type wherein the injected beamdrifts through a magnetroninteraction region to a beam collectorstructure, of arranging the electron gun assembly such that the RFfields on theslow wave circuit may penetrate into the region of theelectron gun for controlling the level of beam current produced by theelectron gun, whereby the radio frequency energy on the slow wavecircuit controls the injected beam current level.

Another feature of the present invention is the same as the precedingfeature wherein the electron gun assembly is of the magnetron injectiontype having an annular thermionic emitter surrounded by an acceleratingelectrode with the axial spacing from the electron gun to the anodecircuit and the spacing from the thermionic emitter to the acceleratingelectrode being dimensioned such that the radio frequency fields on theslow wave circuit may penetrate into the region of the electron gun forcontrolling the current level drawn therefrom into the magnetroninteraction region.

Another feature of the present invention is the same as the firstfeature wherein the electron gun is of the (Hype having a relativelylarge annular beam passage in the accelerating elec trode structurewhich is closely spaced to the slow wave circuit such that the RFfields. on the slow wave circuit may penetrate through the annular beampassage in the accelerat ing electrode into the electron gun forcontrolling the electron beam current drawn from the thermionic emitter.

Other features and advantages of the present invention will becomeapparent upon a perusal of the following specification taken inconnection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic longitudinalsectional view, partly in block diagram form, of an injected beamcrossed-field amplifier employing features of the present invention,

FIG. 2 is a schematic sectional view of a portion of the structure ofFIG. 1 taken along line 2--2 in the direction of the arrows,

FIG. 3 is an enlarged detailed view of a portion of the structure ofFIG. 1 delineated by line 3-3 and depicting the magnetron injectiongunof the present invention,

FIG.4 isan enlarged detail view of a portion of the structure of FIG. 1delineated by line 44 and depicting the type-0 electron gun of thepresent invention, and I FIG. 5 is a plot of injected beam currentversus RF input drive power depicting the increase of beam current withthe increase in input RF drive power.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2,there is shown the injected beam crossed-field amplifier tube 1incorporating features of the present invention. The tube 1 includes acylindrical nonemissive sole electrode 2 surrounded by a cylindricalanode structure including an annular slow wave circuit 3 such asatoroidal helix having an input terminal 4 at one end and an outputterminal 5 at the other end. An annular magnetron interaction region 7is defined by the annular space between the sole 2 and the anodestructure. An axially directed magnetic field B is provided in themagnetron interaction region 7 by means of a magnet structure, notshown. A circuit sever 6 is provided between the ends 4 and 5 of theslow wave circuit 3 to prevent RF feedback from the output terminal 5 tothe input terminal of the helix and to debunch the reentrant stream ofelectrons.

An electron gun assembly 8 is provided at one end of the magnetroninteraction region 7 for injecting a beam of electrons axially into themagnetron interaction region 7 and through the interaction region 7 to abeam collector structure 9 disposed at the other end of the sole 2. Theelectron gun 8 may be either of the magnetron injection type or of the0- type, more fully described below with regard to FIGS. 3 and 4. Avacuum envelope ll encloses the aforedescribed'elements and is evacuatedto a low pressure such as 10" Torr.

A cathode supply 12 supplies a negative potential as of l,l40 volts tothe thermionic emitter of the electron gun 8. An accelerator supply 13supplies a. positive accelerating potential, as of +610 volts relativeto the cathode-potential, to

the accelerating electrode of the electron gun 8. A depressed collectorsupply 14 supplies a positive potential to the collector electrode 9relative to the cathode potential. A suitable depressed collectorpotential is +450 volts. A sole supply supplies a negative potential, asof l40 volts, to the sole electrode 2 relative to the cathode potential.The slow wave structure 3 forms an anode structure and is operated atground potential.

In operation, the electron gun 8 injects a beam of electrons axiallythrough the magnetron interaction region 7 to the beam collector 9.Radio frequency wave energy to be amplified is applied via terminal .4to the slow wave structure 3 for cumulative magnetron-type interactionwith the electron beam to produce an amplified output signal which isextracted from the slow wave circuit 3 at output terminal 5 and fed to asuitable utilization device, not shown. The power flow of wave energy onthe slow wave circuit 3 is orthogonally directed to the drift directionof the electrons as they pass through the magnetron interaction region7. As a result, noise energy in the electron beam is not coupled to theslow wave circuit.

However, the intense electric fields of the slow wave circuit interactwith the beam in the magnetron interaction region to form the beam intospokes of charge which are caused to spiral around the sole electrode 2for cumulative interaction with the RF wave on the slow wave circuit 3.The electron gun 8 is designed such that the radio frequency fields onthe anode slow wave circuit 3 may penetrate into the gun structure 8 tocause the current emitted from the emitter to vary in variableaccordance with the intensity of the RF drive signal applied to the slowwave circuit 3 for amplification amplified. The gun designs are morefully described below with regard to FIGS. 3 and 4. However, as a resultof the RF drive control of the intensity of the injected electron beamthe low noise characteristics of the device are further enhanced in thelow signal regime while permitting relatively high output powers to beobtained in the high power regime. In addition, the efficiency of thetube is improved because the DC power drawn by the tube is reduced inthe low signal regime, thereby substantially increasing the efficiencyof the tube in the low power regime.

Referring now to FIG. 3, there is shown the magnetron injection gun 8incorporating features of the present invention. The gun 8 includes acylindrical thermionic cathode emitter 21, for example, of the dispensertype heated to thermionic emission temperature by means of a heater 22.An annular accelerating electrode 23 concentrically surrounds thecylindrical cathode emitter 21. An electron beam focusing ring 24 isdisposed adjacent to the emitting surface of the cathode emitter 21 atthe upstream end of the beam for causing the electrons to drift into themagnetron interaction region 7. In such an electron gun, a virtualcathode is formed at the plane identified by 25 at the downstream end ofthe thermionic emitter 21.

Electron gun 8 is designed to have a relatively open structure and to berelatively closely spaced to the anode 3 such that the radio frequencyfields from the anode slow wave circuit 3 may penetrate into the regionof the virtual cathode 25 and also into the region of the gun 8 forcontrolling the intensity of the injected beam current.

In a preferred embodiment of the magnetron injection gun 8, the radialspacing d, from the thermionic emitter 21 to the accelerating electrode23 is preferably greater than one-half the radial spacing 11;, from thethermionic emitter 21 to the inside diameter of the slow wave circuit 3.In addition, the axial spacing d from the end of the thermionic emitter21 to the adjacent end of the slow wave-circuit 3 is preferably lessthan the radial spacing from the thermionic emitter 21 to the insidediameter of the slow wave circuit 3. In a typical example, the electrongun 8 had dimensions as shown on FIG. 3 and produced an RF control overthe beam current as shown in FIG. 5. More specifically as shown in FIG.5, with an input RF drive power of one-tenth of a watt the beam currentwas approximately 60 ma., whereas at an input drive power of 40 wattsthe beam current was 150 ma., thus, representing a substantial RFcontrol over the beam current.

Referring now to FIG. 4, there is shown the type-O electron gun 8incorporating features of the present invention. In this embodiment, thegun 8 includes an annular thermionic emitter 31 as of thedispenser typeheated to thermionic emitting temperature by means of a heating element32. The annular emitter 31 is axially aligned with the annular magnetroninteraction region 7. An annular beam focusing electrode structure 33axially projects toward the magnetron interaction region 7 for focusingthe beam emitted from the emitter 31 through an annular beam passageway34 in an accelerating electrode 35. In this embodiment, the radialdimension d of the annular beam passageway 34 in accelerating electrode35 is preferably greater than one-half the radial thickness of themagnetron interaction region d,,. In addition, the axial spacing d fromthe slow wave structure 3 to the accelerating electrode 34 is preferablyless than the radial thickness d of the magnetron interaction gap 7. Asa result, a relatively open electron gun structure 8 is provided suchthat the radio frequency fields on the slow wave structure 3 maypenetrate through the beam passageway 34 into the region of the gun 8for controlling the electron current drawn from the emitter 31 in use.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What we claim is:

1. The method for controlling the beam current level in an injected beamcrossed-field amplifier tube comprising the steps of, subjectingelectron emitted from a thermionic cathode to an accelerating field toproduce a beam of electrons which is passed axially through an annularmagnetrontype interaction region defined between a curved andnonreentrant slow wave circuit operating at anode potential and aconcentrically disposed nonemitting cathode sole electrode, collectingthe beam after passage thereof through at least a portion-of themagnetron-type interaction region, applying a radio frequency signal tothe slow wave circuit for cumulative interaction between the radiofrequency energy on the slow wave circuit and the beam of electrons toproduce an amplified output radio frequency signal, TI-IE IMPROVEMENTCOMPRISING, causing the radio frequency fields on the anode slow wavecircuit to penetrate into the region of the electron beam producingaccelerating fields to cause the electron current drawn from thethermionic emitter to increase with an increase in the intensity of theradio frequency signal energy on the slow wave circuit, whereby the beamcurrent level is controlled by the intensity of the input signal to beamplifier.

2. In an injected beam crossed-field amplifier tube, means forming anonemitting sole electrode structure, means forming a curved anodestructure concentrically surrounding said sole electrode to define anannular reentrant stream magnetron-type interaction region therebetween,said anode structure including a curved slow wave circuit portion and acircuit sever portion, means forming a thermionic electron gun structuredisposed at one axial end of the annular magnetron interaction regionfor injecting a beam of electrons axially through the annular magnetroninteraction region for cumulative interaction with radio frequency waveenergy on the slow wave circuit to produce an output signal, meansforming an electron collector for collecting the beam after passagethereof through the interaction region, TI-IE IMPROVE- MENT WHEREIN, thespacing from said thermionic electron gun to said slow wave circuit isdimensioned sufficiently close such that the radio frequency fields onthe slow wave circuit penetrate into the region of said thermionicelectron gun to cause the electron current level injected into saidmagnetron type interaction region to increase and decrease in variableaccordance with increases and decreases in the radio frequency powerlevel on said slow wave circuit, whereby the radio frequency energy onsaid slow wave circuit controls the injected beam current.

3. The apparatus of claim 2 wherein said electrongun structure is amagnetron injection gun including, an annular thermionic cathode emittercoaxially aligned with said nonemitting sole electrode, means formingan'electron accelerating electrode concentrically disposed surroundingsaid thermionic emitter with a radial spacing from the emitting surfaceof said emitter greater than one-half the radial spacing from theemitting surface of said emitter to the inside diameter of said slowwave circuit, and the axial spacing from said gun to said slow wavecircuit being less than the radial spacing from said emitter to saidslow wave circuit.

4. The apparatus of claim 2 wherein said electron gun includes, anannular thermionic cathode emitter coaxially aligned with the annularmagnetron-type interaction region,

means forming an accelerating electrode structure axially spaced fromsaid emitter and disposed between said cathode emitter and the magnetroninteraction region, said accelerating electrode having an annular beampassageway therein for passage of the beam therethrough into themagnetron-type interaction region, the radial dimension of said annularbeam passageway in said accelerating electrode being greater thanone-half the radial thickness of the magnetron interaction region toprovide a relatively open electron gun structure, and the axial spacingfrom said slow wave structure to said electron gun being less than theradial thickness of said magnetron-type interaction gap.

1. The method for controlling the beam current level in an injected beamcrossed-field amplifier tube comprising the steps of, subjectingelectron emitted from a thermionic cathode to an accelerating field toproDuce a beam of electrons which is passed axially through an annularmagnetron-type interaction region defined between a curved andnonreentrant slow wave circuit operating at anode potential and aconcentrically disposed nonemitting cathode sole electrode, collectingthe beam after passage thereof through at least a portion of themagnetron-type interaction region, applying a radio frequency signal tothe slow wave circuit for cumulative interaction between the radiofrequency energy on the slow wave circuit and the beam of electrons toproduce an amplified output radio frequency signal, THE IMPROVEMENTCOMPRISING, causing the radio frequency fields on the anode slow wavecircuit to penetrate into the region of the electron beam producingaccelerating fields to cause the electron current drawn from thethermionic emitter to increase with an increase in the intensity of theradio frequency signal energy on the slow wave circuit, whereby the beamcurrent level is controlled by the intensity of the input signal to beamplifier.
 2. In an injected beam crossed-field amplifier tube, meansforming a nonemitting sole electrode structure, means forming a curvedanode structure concentrically surrounding said sole electrode to definean annular reentrant stream magnetron-type interaction regiontherebetween, said anode structure including a curved slow wave circuitportion and a circuit sever portion, means forming a thermionic electrongun structure disposed at one axial end of the annular magnetroninteraction region for injecting a beam of electrons axially through theannular magnetron interaction region for cumulative interaction withradio frequency wave energy on the slow wave circuit to produce anoutput signal, means forming an electron collector for collecting thebeam after passage thereof through the interaction region, THEIMPROVEMENT WHEREIN, the spacing from said thermionic electron gun tosaid slow wave circuit is dimensioned sufficiently close such that theradio frequency fields on the slow wave circuit penetrate into theregion of said thermionic electron gun to cause the electron currentlevel injected into said magnetron type interaction region to increaseand decrease in variable accordance with increases and decreases in theradio frequency power level on said slow wave circuit, whereby the radiofrequency energy on said slow wave circuit controls the injected beamcurrent.
 3. The apparatus of claim 2 wherein said electron gun structureis a magnetron injection gun including, an annular thermionic cathodeemitter coaxially aligned with said nonemitting sole electrode, meansforming an electron accelerating electrode concentrically disposedsurrounding said thermionic emitter with a radial spacing from theemitting surface of said emitter greater than one-half the radialspacing from the emitting surface of said emitter to the inside diameterof said slow wave circuit, and the axial spacing from said gun to saidslow wave circuit being less than the radial spacing from said emitterto said slow wave circuit.
 4. The apparatus of claim 2 wherein saidelectron gun includes, an annular thermionic cathode emitter coaxiallyaligned with the annular magnetron-type interaction region, meansforming an accelerating electrode structure axially spaced from saidemitter and disposed between said cathode emitter and the magnetroninteraction region, said accelerating electrode having an annular beampassageway therein for passage of the beam therethrough into themagnetron-type interaction region, the radial dimension of said annularbeam passageway in said accelerating electrode being greater thanone-half the radial thickness of the magnetron interaction region toprovide a relatively open electron gun structure, and the axial spacingfrom said slow wave structure to said electron gun being less than theradial thickness of said magnetron-type interaction gap.